Possible 177 cal Regged Mrod2 Build?

[FuzzyGrub]

Hole drilled and assembled for first pressurization. First bump. I proved that the vent hole works! Lots of air, wouldn't start to pressurize.

No gouges in o-ring, thought internal o-ring in reg was out of place. Reassembled, still massive venting. Reg adjusted to zero?

[SHOOTINIT]

I wasn't sold on the vent hole regs.

[FuzzyGrub]

It was set to 2 turns ccw from full cw (just touching). That wouldn't seem to be problem. Washers are all paired up, and both internal O-rings look good.

Adjustment notes from Roy: Easy to adjust, unlock the nut, ccw to increase and cw to decrease,1/4 turn about 190 to 200 psi. i think I set about either 1600 or 1800 psi.

So 2 turns out should be about 1600 psi.

I don't have a good understanding of how it works which is complicating the debug. Not sure how air gets in the outer chamber with the washers to the vent hole, but it obviously is. hmmm.

[FuzzyGrub]

OK, found the issue! Under a magnifying glass I found a flat spot/slice in the larger of the two internal O-rings. Replaced with spare in kit, and it pressurized to 3K. Crosman gauge is reading 2k instead of 1.6k, but that should just be an adjustment to reg.

PS: I'll need to get the sizes of the two internal O-rings.

[FuzzyGrub]

The gun gauge was reading 200psi high compared to tank gauge. Adjusted reg cw 1/4" turn, and gauge reads 1.8k which should equal 1.6K.

Continue on.

[SHOOTINIT]

how jumpy is the gauge when you shoot?

[FuzzyGrub]

A couple more snags. I hadn't noticed that the gauge ext changed for Mrod II. It is a little shorter. I used one that I had from a Mrod I, so it is sticking out of the stock by a quarter inch or so.

The CF sleeve that I used has a OD slightly more than 1/2". Sanded it to fit for an tight fit in the breach. Shroud pieces won't fit (for now).

I took a few (loud) shots over the chrony (no scope). 900fps w/10.3g jsbs. The striker is full ccw from the install and the preload was only 1 T cw, with velocity screw at 5T out.

[FuzzyGrub]

Glued the CF sleeve to barrel and will need to cure for some time. I will order the correct gauge ext in the AM.

[FuzzyGrub]

Got her back together this evening. Back with the Mrod 177 barrel, since the challenger LW barrel wasn't going to work for me. http://www.marauderairrifle.com/forum/viewtopic.php?f=32&t=10246 Shot the 1st complete string. Filled to 3K psi and had about 68 shots before going off reg (below 1600 psi). The 1st 7 shots seem to come up a slight curve, but settled out after that. Is it just the reg settling out, or does higher pressure have some impact on reg operation? 61 shots between 896 and 903 fps w/JSB 10.3g.

Not sure how to tune a reg gun. Do you mainly focus on the off reg curve to maximize shot count? ie get a slight bell curve coming off reg.

Spring makes the most noise and seems more than normal. I think that is side effect of light hammer.

Accuracy of the 177 barrel not where I want it. Once I am credited with the challenger barrel, will spin the barrel wheel of fortune.

[Motorhead]

Polish the ends of hammer spring and make sure it has no sharp corner on ends of last coil
Oddly with the light hammers, some get spring buzz and some don't ... spring alignment or canting issues no doubt.

As to maximizing shot count ... you adjust Reg output pressure pending if velocity rises or falls coming off the set point.
* If velocity RISES .... Lower Regs set point and back off spring tension resetting to ideal velocity. ( Lower pressure allow easier valve opening so less hammer strike will be required )
Now you will be shooting to lower pressure when it comes off the reg and will have less hammer strike too so a spike in velocity does not happen.

* If velocity FALLS coming off the reg ... reverse that above

Balance it correctly the rifle will shoot and come off the Reg right under the apex of bell curve ... ideally rise no more than 1%, level off and then fall away.